This invention relates generally to frequency control of laser emitted radiation.
A generally known method for stabilization of laser frequency, with which the present invention is associated, involves the Stark effect wherein an electric field applied to a radiation absorbing medium acts to change its atomic or molecular energy state reflected by corresponding spectral and absorption lines. Heretofore, a small fraction of a laser emission was directed through a body of the absorbing medium selected because of maximum absorption corresponding to the desired frequency at which the laser is to be stabilized. An error signal was generated by phase comparison of oscillatory modulations of the DC electric field, establishing the maximum absorption state of the absorbing medium, in order to correct deviation from the stabilization frequency by adjustment of the resonator cavity length of the laser generator through which laser frequency is determined.
Although the foregoing method of frequency stabilization is precise, the Stark effect absorption of laser radiation by the absorbing medium was typically limited to one or a few absorption lines thereby limiting the number of corresponding frequencies capable of being stabilized by a single absorption cell. The degree of variation in absorption coefficients furthermore created problems in connection with any absorbing medium having more than one usable absorption line.
It is therefore an important object of the present invention to provide a radiation absorption cell employing the Stark effect to stabilize operation of a laser with respect to a plurality of emission frequencies in a precise and rapid manner without the problems and complexities heretofore experienced.
A further object of the invention is to provide a single Stark effect absorption cell through which a corrective adjustment process may be effected to stabilize a plurality of different emission frequencies between which laser operation may be rapidly switched, without clutter or interference.